DENSITY  OF  MOLTEN  GLASS 


BY 


SHEO-HEN  El 


THESIS 


FOR  THE 


DEGREE  OF  BACHELOR  OF  SCIENCE 

IN 

CHEMICAL  ENGINEERING 


COLLECE  LIBERAL  ARTS  AND  SCIENCES 


UNIVERSITY  OF  ILLINOIS 


1922 


■ 


■ 


' 


i 


ACKN  OWLEDGMEUTS 
******* 

The  writer  v?ishes  to  take  this  opportunity  to  express 
his  appreciation  of  the  guidance  and  help  that  Professor  E.W. Wash- 
bum  has  so  kindly  given. 

He  also  wishes  to  express  his  appreciation  for  the  help 
given  by  Dr .E. IT. Bunting  in  the  preparation  of  this  thesis. 


************* 


Digitized  by  the  Internet  Archive 
in  2015 


https://archive.org/details/densityofmoltengOOIish 


TABLE  05’ 


CONTENTS 


Page 

I.  INTRODUCTION 1 

II . EXPERIMENTAL  PART.  2 

III.  CALIBRATION  OF  THE  SPRING 5 

IV.  CALCULATIONS... 7 

V.  RESULTS  FROM  EXPERIMENTS 9 

VI.  DISCUSSION 11 

1 . Suggestions 13 

VII . SUMMARY • 14 


-1- 


DENSITY  OF  MOLTEN  GLASS 

■X-W-W  X‘  k X'  Ar  X : 'k  k '{-if  -jf  k )’;  vif  X* 

I.  INTRODUCTION 

The  importance  of  tne  determination  of  the  density  of 
molten  glass  can  be  discussed  from  two  aspects.  First,  from  the 

purely  scientific  point  of  view,  and  secondly,  from  the  practical 
(point  of  view. 

The  art  of  glass  making  has  been  known  since  ancient  times. 
But  since  then  there  has  not  Been  very  much  advancement  until  rather 
modern  times.  People  now-a-days  know  how  to  make  glass,  but  the 
reactions  in  various  steps  during  its  course  of  manufacture  are  not 
completely  known.  Only  little  work  has  been  done  on  the  various 
properties  of  glass  at  high  temperatures.  No  work  has  been  done 
on  the  density  of  molten  glasses.  Thus  although  the  art  of  glass 
manufacture  is  quite  perfect,  yet  the  knowledge  of  its  underlying 
! facts  is  still  incomplete.  Work  of  this  kind  will,  of  course,  be 

of  some  value  for  the  literature. 

From  the  practical  point  of  view,  density  has  a close 
1 relation  with  viscosity,  surface  tension,  and  other  physical  constant 
By  knowing  the  densities  at  high  temperatures,  we  can  figure  out 
the  coefficient  of  expansion  at  different  temperatures.  This  work 
has  been  carried  on  to  600°C  by  C.G. Peters  and  C.H.Cragoe.* 

* 

J.Opt.  Soc.Am.4,  105-44,  1920 


-2- 


The  density  of  molten  glass  is  an  important  factor  in  the  process 
of  feeding  the  molten  glass  to  the  molds  or  machines  for  making 
different  articles. 


-3- 

II.  EXPERIMENTAL  PART. 

The  method  used  for  the  determination  of  the  density  of 
molten  glass  was  to  immerse  a platinum  sphere  of  known  volume  in  tie 
fluid  , and  the  loss  of  weight  was  measured  . The  density  was  then 

obtained  by  a simple  process  of  division  with  a few  necessary 
corrections.  The  sphere  was  suspended  on  a Jolly  spring  balance 
iwith  a fine  platinum  wire.  In  order  to  diminish  the  effect  of 
jsurface  tension,  which  was  one  source  of  error,  as  much  as  possible, 
and  at  the  same  time  to  have  the  wire  strong  enough  to  nold  the 
weight  at  high  temperatures,  wire  of  0.3  mm.  in  diameter  was  used. 
The  furnace  was  heated  by  electricity  by  passing  current  through 
a platinum  resistance  coil.  As  shown  on  the  diagram,  the  furnace 
consists  of  a long  porcelain  cylinder  writh  platinum  heating 
element  wound  outside.  The  glass  pot  in  which  the  glass  was  melted 
was  of  similar  construction,  but  smaller  in  size  so  that  it  would 
just  fit  into  the  furnace.  One  more  porcelain  pot  a little 
larger  than  the  heating  pot  was  used  to  protect  the  latter  and 
facilitate  the  task  of  mending  in  case  any  accident  happened  to  the 
furnace.  ho w the  whole  apparatus  was  put  in  a large  fire  clay 

cylinder  containing  a lot  of  insulating  materials,  such  as  silocel 
and  calcined  kaolin.  In  order  to  prevent  radiation  loss  on  the 

top,  a well  fitted  porcelain  cover  was  used.  The  cover  consisted 
of  two  equal  semi-circular  discs  with  a hole  in  the  center  so  that 
we  could  see  what  was  going  on  during  the  run.  The  temperature 
was  measured  by  a plat inum- rhodium  thermocouple  inserted  between 

^ ^ ~ 1 — ^ ■— — —— — — i 


the  glass  pot  and.  the  heating  cylinder.  how  the  glass  in  small 
pieces  was  charged  into  the  pot  with  the  thermocouple  fitted  in 
position,  and  the  current  turned  on.  After  the  glass  136031116 
quite  fluid  the  platinum  hall  was  inserted.  Care  was  taken 

not  to  immerse  too  much  of  the  wire  beneath  the  surface,  but  just 
enough  so  that  the  ball  was  completely  immersed.  The  temperature 
of  the  glass  was  raised  to  a little  above  1400°C  and  icept  at  this 
temperature  for  a few  moments  in  order  to  secure  equilibrium. 

Then  readings  were  ready  to  be  taken.  The  distance  or  stretch 
between  two  definite  points,  A and  B ( see  the  diagram)  on  the 
spring  was  read  by  means  of  a cathetometer  to  0*02  mm.  Headings 
were  taken  at  1200°,  1300°,  and  1400°  respectively.  A reading 
was  first  made  at  1400°,  and  then  the  furnace  was  coded  down  very 
slowly  to  1300°C,  maintained  at  this  temperature,  when  another 
reading  was  taken.  A similar  reading  was  made  a„t  1200°C.  After 

this,  the  temperature  was  again  raised  and  another  set  of  readings 
obtained  in  order  to  check  the  first  set  of  readings. 


? A 


Spring 


i 


porce  i ion  Insu  /at'ors 


P/ohnam  boll 


Fire  brick 


PI  a bin  um 
suspension  wire 

glass  pot 

, Platinum 

heating  e/errjenh 


O l 


• \ 
• \ 
• « 

t t 

^ ; > 
' * 

i ; 

mil 

m 

IBjTY1.  vviV/ 

'U 


Molten  g/ass 
Si/oce/  insulation 

X 

Fire  c/ay  cy/inoter 


FURNACE  AND  SPRING  FOR  THE 
DETERMINATION  OF  THE  density 
OF  MOLTEN  GLASS 


V*  v • . ■ 


^\»r\v\  ,\'  . 

V ' :■>  <\f.  \v,\  y.,.  hxrt 


V v:  f.  . t>\c , 
rA'WW.  \ 


S>1? 


Ws  V Vo  ^ ^ ',  iV-A.-' 


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7' , i 3 . ':-7  7.7  ■ 7VFv7  t. 


-5- 

III.  CALIBRATION  OR  THE  SPRING. 

The  spring  was  calibrated  by  applying  to  it  successively 
a series  of  known  weights,  and  at  each  time  after  the  spring  came 
to  rest,  the  amount  of  stretch  between  the  points  A and  B on  the 
spring  was  read,  a,nd  the  amount  of  elongation  by  one  gram  additional 
weight  was  obtained  by  averaging  all  the  readings. 

Table  I shows  a calibration  of  the  spring  used. 


Table  I 


Weight 
on  spring 

i 

10  gm. 

10.5 

11 

11.5 

12 

12.5 

13. 

Upper 

reading 

104.082 

104.082 

104.082 

104.082 

104.082 

104. 082 

104.082 

Lower 

reading 

80.764 

80.320 

79.880 

79.435 

78.986 

75.543 

77.095 

Total 

Stretch 

25.318 

23.762 

24.202 

24.647 

25.096 

25.537 

25.987 

Elonga- 

tion 

0.444 

0.440 

0.445 

0 .449 

0.441 

0.437 

The  wt . of  the  pan  (0.5956  gm.)  used  for  holding  the  weights 
was  not  included  on  the  table  because  what  we  wanted  was  the  elonga- 
tion of  one  gram  weight.  The  weight  of  the  pan  w as  measured 
because  it  had  to  be  included  for  the  calculation  of  the  check 
weight. 

Nov/  immediately  after  finishing  each  determination,  the 
weight  of  the  platinum  ball  in  the  molten  glass  was  calculated  by 
means  of  this  table  and  a metal  button  of  any  kind  having  its 
weight  equal  to  the  calculated  value  wss  weighed  out.  Without 


- 6 - 

letting  the  spring  go  back,  the  platinum  ball  with  its  suspension 
wire  was  removed  from  the  spring  and  the  check  weight  put  on  it. 
After  the  spring  came  to  rest,  the  reading  of  the  stretch  between 
the  points  A and  B on  the  spring  was  again  made. 

By  comparing  this  amount  of  stretch  with  that  of  the  actual  run, 
the  difference  was  interpolated  and  added  or  subtracted  from  the 
known  weight,  as  the  case  may  be.  In  this  way  any  source  of 

error  euch  as  that  due  to  fatigue  of  the  spring,  or  to  change  of 
temperature  of  the  spring  tending  to  alter  the  amount  of  stretch 
from  its  normal  value,  was  eliminated 


. 


< 


< 

. 


-7- 


IV.  CALCULATIONS 

Tne  volume  of  the  platinum  ball  was  obtained  by  Archimede' s 
water  displacement  method.  If  the  water  in  which  the  platinum 
ball  was  weighed,  were  at  4°C,  then  loss  of  weight  in  water  would 
give  us  its  volume  directly.  But  if  it  were  not  at  4°C,  the  loss 
was  divided  by  the  density  of  water  at  the  corresponding  temperature. 
Necessary  corrections  were  applied  to  the  calculation.  The  volume 
of  the  platinum  ball  at  high  temperatures  was  obtained  by 
applying  the  following  equation: 

V » ( 1 + at)  V0 

where  V = the  volume  at  temperature  = t 

t 

V = Volume  of  platinum  ball  at  0° 

o 

CX  = the  cubical  coefficient  of  expansion 
The  volume  of  the  platinum  ball  calculated  from  the  above  equation 
at  temperatures  1200°,  1300°  and  1400°C  was  0.6056,  0.6064,  and 
0.6030  cc,  respectively.  After  securing  the  readings  at  various 
temperatures,  the  weights  corresponding  to  the  stretches  were 
calculated  and  a check  weight  of  metal  having  the  same  weight  was 
applied  to  the  spring.  from  this  we  obtained  the  true  weight 
of  the  platinum  ball  in  glass  with  one  more  correction,  i.e.  the 
Surface  tension  effect  of  the  molten  glass,  which  was  exerted  on 
the  suspension  wire  and  helped  to  pull  down  the  spring.  The  sur- 
face tension  of  the  glasses  was  determined  by  Mr .E.E.Libman  in 
his  doctorate  thesis,  and  it  varies  from  140  to  170  dynes  per 

Since  this  was  not  a big  amount  the  average  value 


centimeter. 


-8- 

of  155  dynes  per  centimeter  was  used  in  this  case.  The  following 

formula  was  used  in  calculating  the  results: 

Density  = Wt . in  air  -(Wt.in  glass-Surf ace  tension  corr.) 

Volume  of  tn*e  pt  / FalV  ’ 

The  density  of  thirteen  samples  of  glass  having  the  following- 
composition  was  determined. 


TABLE  II.  Composition  of  the  Glasses 


No. 

SiO 

2 

Na  0 
2 

CaO 

2 

82.3 

17.7 

3 

70.0 

30.0 

4 

60  • 0 

40.0 

5 

62.7 

14.7 

22.6 

6 

60.5 

20.0 

19.5 

7 

60 

30 

10 

8 

70 

20 

10 

9 

52.5 

40.0 

7.5 

10 

70.0 

10 

20 

12 

72 

14.5 

13.5 

13 

73.5 

16.5 

10.0 

15 

67.5 

15.5 

17.0 

16 

65 

20 

15.0 

The  results  from  the  experiments  are  tabulated  as  follows: 


-10 


In  order  to  make  the  results  easily  understood,  two  other 
methods  as  given  below  were  used,  (a)  by  the  temperature  density 
curves  and  (b)  by  the  composition  density  model. 

(a)  The  curves  were  all  drawn  to  the  same  scale  so  as  to 
give  a better  comparison.  One  extra  curve  was  drawn  for  glass 
No.16.  In  this  case  a duplicate  was  run  and  more  frequent 
density  readirgs  were  taken  at  smaller  temperature  intervals. 

This  curve  shows  a maximum  density  at  1380°C, 

(b)  The  composition  density  model  was  built  for  the  density 

of  the  different  glasses  at  1420°C.  The  composition  of  the 

glass  is  represented  on  the  triangular  coordinate  paper.  The 
vertical  distance  of  the  model  at  any  point  represents  the  density 
at  1420°  of  the  glass,  having  its  composition  represented  by  the 
point.  Each  centimeter  vertical  distance  of  the  model  repre- 

sents an  amount  of  0.1  for  the  density.  As  shown  on  the  photo- 
graph attached  below,  the  first  white  horizontal  line  represents 

a density  of  2.15;  the  second  2.2,  etc.,  The  base  of  the  model 
represents  a density  of  two. 


200  400  600  800  /OOO  / 200  /40O 


o(H>/ oo?/  000/ 00‘S  009 00^/  __  oo? 


. 


200  ~ 400  goo  goo  /ooo  /200  /4oo 


1200  1250  BOO  /J50  !*oo  /450 


-11  - 


VI.  DISCUSSION. 

Accuracy  of  the  Result.-  The  results  do  not  show  much 
uniformity  in  the  amount  of  expansion  from  room  temperature  to  1400°C 
nor  do  they  show  any  indication  of  the  relation  "between  the 
composition  of  the  glass  and  the  amount  of  expansion.  The  dupli- 
cates run  f or  a few  samples  only  check  to  the  second  place  after 
the  decimal.  small  errors  are  unavoidable  in  making  readings 

of  temperature  and  elongation.  Dissolved  gases  in  glass  have 
considerable  effect  upon  the  experiment.  This  difficulty,  however, 
could  be  overcome  by  putting  the  molten  glass  under  vacuum  so  as  to 
lift  the  gas  out  of  the  mass.  But  another  source  of  gas  buble 
may  arise  from  the  decomposition  or  volatilization  of  certain 
components  of  the  glass.  This  is  shown  by  an  experiment  with 

lead  flint  glass.  The  density  of  the  lead  flint  glass  was 

determined.  When  the  temperature  reached  1300 °C  , gas  bubbles 
began  to  appear,  and  as  the  temperature  went  up  more  gas  bubbles 
appeared.  At  the  same  time  the  platinum  ball  was  raised  up 

considerably.  This  probably  was  due  to  the  gas  bubbles  adhering 
to  the  ball  and  tending  to  rise  up  to  the  surface.  As  the 

temperature  coded  down  again,  the  ga.s  bubbles  disappeared  gradually 
until  at  1200°C  no  more  bubbles  were  visible.  This  phenomenon 
perhaps  was  due  to  the  vaporization  of  arsenic  compounds  at  high 
temperature.  Difficulties  of  this  kind  may  not  be  a-le  to  be 
overcome  without  changing  the  composition  of  the  glass.  Still 
another  source  of  gas  bubbles  may  be  due  to  the  excluded  gases 


- 


. 

-12- 

in  platinum  escaping  at  high  temperature.  In  high  silica  glasses 
the  melting  range  is  so  high  that  the  glass  is  still  very  viscous 
at  1200°C  or  1300°C*  and  it  is  no  doubt  difficult  to  obtain  reliable 
measurements  under  these  circumstances.  For  these  reasons  it  is 
not  expected  that  the  results  are  very  accurate.  Since  the 
duplicates  of  a few  samples  check  to  the  second  place  after  the 
decimal,  the  third  place  after  the  decimal  shown  in  the  table  is  not 
of  much  value. 

Glasses  No.  4 and  No.  16  show  a peculiar  phenomenon,  i.e., 
as  the  temperature  goes  up  the  density  goes  up  also.  A duplicate 
was  run  on  glass  No.  16  and  the  readings  check  fairly  well. 

The  temperature  density  curve  of  glass  No.  16  shows  a maximum  at 
1380®C.  This  may  be  due  to  certain  errors,  but  since  the  two 
runs  check  it  is  not  likely  that  any  errors  made  are  merely  coin- 
cident. Whether  or  not  glasses  do  have  this  property  needs 

further  investigation. 

Jaeger  in  Holland  used  a balance  suspended  over  the  fur- 
nace in  determining  the  density  of  molten  salts.  The  platinum  ball 
was  suspended  f r an  the  bottom  of  the  pan,  the  other  arrangements 
being  similar  to  those  described  above.  This  method  may  take 
longer  time  to  get  equilibrium.  The  spring  suspension  method  has 
the  advantage  of  simplicity  and  ease  of  manipulation.  The  sources 
of  error  due  to  any  effect  tending  to  alter  the  amount  of  elongation 
from  the  normal  value  can  be  eliminated  by  immediate  checking  after 
each  run.  Tne  disadvantage  of  this  method  is  that  if  the  two 
telescopes  are  not  set  quite  parallel,  e.  small  angle  will  maxe 
considerable  error  in  the  result. 


13  - 


Suggestions;  - Evacuate  every  glass  before  each  experi- 
ment. Keep  the  molten  glass  at  a certain  temperature  long  enough 
in  order  to  secure  equilibrium  before  a reading  is  taken. 

Run  the  temperature  up  and  down  through  the  range  at  least  twice  in 
order  to  see  if  the  readings  check. 

Lastly  take  good  care  in  leveling  the  two  telescopes  so  that  they 
are  exactly  parallel.  In  this  way  readings  checking  to  the  third 
place  after  the  decimal  might  be  obtained. 


. 


- 14  - 


VII.  SUMMARY 

(a)  The  range  of  expansion  of  different  soda-lime  glass 
from  room  temperature  to  1400°C  is  from  2.49$  to  14.8$. 

(b)  The  errors  in  the  experiment  are  mostly  due  to  the 
behavior  of  the  glass  at  high  temperature  and  can  be  removed  by 
evacuating  the  glass  and  by  prolonged  heating. 

(c)  Whether  or  not  the  molten  density  has  a maximum  point 
of  density  needs  further  investigation. 


